1. Field of the Invention
The present invention relates to adjustable impedance matching networks, and more particularly, an adjustable impedance matching network of either a T or Pi-type which employs a fixed value capacitor or inductor at either the input or output sides of the network.
2. Discussion of the Prior Art
Impedance matching networks are known and are used to establish a condition in which the impedance of a load is equal to the conjugate of the internal impedance of the source. This condition of impedance matching provides for the maximum transfer of power from the source to the load. In a radio transmitter, it is desired to deliver maximum power from the power amplifier to the antenna. Maximum power is transferred from a source to a load, at a given frequency, when the load impedance is equal to the conjugate of the generator impedance. Generally, however, the load impedance will not be the proper value for maximum power transfer, and varies, for example, with frequency, ambient temperature, ground moisture and the like. An impedance matching network is inserted between the load and the source to present to the source an impedance that is the conjugate of the generator impedance.
Prior-art impedance matching networks of the T or Pi-type generally employ variable capacitors and inductors. These old impedance matching networks can be easily mistuned, resulting in excess network power loss, excess inductance current, excess capacitor voltages, and decreased bandwidth, thus causing increases in the matching network losses, and excessive current and voltage.